Apparent Malfunction of Demand Pacemaker Caused by Nonpropagated (Concealed) Ventricular Extrasystoles

¹ Section of Cardiovascular Medicine, University of California School of Medicine at Davis, California; Sacramento Medical Center, Sacramento

An example of apparent malfunction of an implanted R-wave-inhibited demand pacemaker is described. The pacer arrhythmia was characterized by slowing, with lengthening of spike-to-spike cycles from the preset value of 0.86 sec (heart rate 70) to as long as 1.34 sec (heart rate 43). Spike-to-spike intervals containing visible PVB's were uniformly longer than 1.34 sec. At times, the pacer was completely inactivated and the heart was controlled entirely by conducted impulses from the fibrillating atria. Both the sensing and the pulse generating circuits of the pacemaker were found to be free of malfunction. The slowing was shown to be the result of concealed ventricular extrasystoles occurring within 0.48 sec of the preceding pacer discharge. Though they failed to propagate to the entirety of the ventricular myocardium and produce visible QRS complexes, they were able to generate sufficient electrical energy, perhaps within the Purkinje fibers and the myocardium immediately surrounding the electrode, to recycle the pacemaker. The pacemaker in this case proved instrumental in documenting the existence of the otherwise elusive entity of concealed ventricular extrasystole. It is suggested that concealed ventricular extrasystoles should be considered in cases of pacemaker slosing and appropriate measures aimed at suppressing premature ventricular beats instituted before decision for replacing the pulse generator is reached.